A shift control device for a vehicle has been known including a parking lock device for switching rotational teeth, rotatable with wheels, into a lock state for a lock tooth to mesh with the rotational teeth and an unlock state for the lock state to be released. To this end, a so-called shift-by-wire (SBW) system is employed for electrically switching shift positions, associated with the running of a vehicle, into the lock state and the unlock state by actuating an actuator provided with the parking lock device in response to a request signal. If an operated position in a shift operation device, operated by a driver, i.e., a shift position is a position for parking (parking position; P position), then, a control signal is output to the parking lock device for mechanically blocking the rotations of drive wheels. This results in actuation of the actuator of the parking lock device such that the rotations of the wheels are blocked. Such a shift control device for the vehicle is disclosed in, for instance, Patent Document 1.
The parking lock device which is caused to actuate by the shift control device disclosed in Patent Document 1 includes the actuator and an encoder. The parking lock device is configured to turn and reciprocate between the P position (parking position; lock position) in which the lock state is established and the non-P position (non-parking position; unlock position) in which the unlock state is established, in accordance with an operation of the actuator. In addition, the parking lock device has structural walls which may perform as stroke ends provided at the P position and the non-P position of the parking lock device, respectively.
The encoder is not of the type that detects an absolute position of the actuator but includes a rotational angle sensor that outputs pulses in conjunction with the rotation of the actuator. Accordingly, if a device power supply is interrupted due to the turn-off of an ignition switch or the like, the shift control device loses information on the absolute position of the actuator. If the power supply is turned on again, therefore, a need arises for recognizing whether an initial switching position of the parking lock device at an original power-on state of the power supply is in the P position or the non-P position.
In the shift control device disclosed in Patent Document 1, therefore, for instance, the switching position, appearing immediately before the power supply is interrupted, is stored in a non-volatile storage device to keep a memory such that information (switching position information) on the switching position in the P position or the non-P position is kept when the power supply is turned off. If the power supply is turned on again and the driver performs a run-enable operation to enable the vehicle to run such as turning on the vehicle power switch (ignition switch), then, the shift control device reads switching position information stored in the non-volatile storage device. In this moment, if the switching position, appearing immediately before the power supply is turned off last time, is in the P position, then, the shift control device allows the actuator to turn to the stroke end associated with the P position for executing P-wall position detecting control for recognizing the position of the stroke end (P wall) associated with the P position. If the switching position, appearing immediately before the power supply is turned off last time, is in the non-P position, then, the shift control device allows the actuator to turn to the stroke end associated with the non-P position for executing non-P wall position detecting control for recognizing the position of the stroke end (non-P wall) associated with the non-P position.
As set forth above, basically, an information about whether the switching position (switching position information) is in the P position or the non-P position is stored in the non-volatile storage device but it may occur that such switching position information does not indicate either the P position or the non-P position and indicates unknown (uncertain). For instance, if the shift control device is terminated in failure during the last turn-off of the power supply, the switching position information is stored to indicate unknown in the non-volatile storage device. If such switching position information indicates unknown in such a way, a vehicular control device, other than the shift control device, is configured to determine the switching position information based on a vehicle speed. This allows the shift control device to receive the switching position information, determined based on the vehicle speed, for executing the P wall position detecting control or the non-P wall position detecting control based on such switching position information. Accordingly, if shift position information, stored in the non-volatile storage device, is unclear, a need arises for the vehicular control device to take a further large number of steps, like those in which shift position information is determined based on the vehicle speed and received to the shift control device, in contrast to a case wherein shift position information indicates the P position or the non-P position. This results in a further increase in time required for the P wall position detecting control or the non-P wall position detecting control to be completed after the run-enable operation is executed. By so doing, the shift control device recognizes if such initial switching position is in the P position or the non-P position.